This invention pertains generally to valves, and more particularly to valves for controlling lubricant injection into a viscous material flow in a pipeline.
Various pumps have been used to pump viscous materials through a pipeline. The viscous material being pumped may be homogeneous or non-homogeneous, may be compressible or incompressible, and may contain significant solid or gaseous content. Such viscous materials include in particular sludge, concrete, and similar materials. When piping such viscous materials through a pipeline, the flow generally occurs as a plug having a relatively uniform cross-sectional velocity profile. A large portion of the force required to pump the viscous material (i.e., back pressure/head loss) is due to frictional effects between the plug of material and the pipe. In order to reduce these frictional losses, lubricating fluids such as water have been added along the edge between the viscous material plug and the pipeline. Such a lubricant injection system is shown in copending application Ser. No. 08/070,516 to Crow et al. for Sludge Pipeline Lubrication System, which is incorporated herein by reference.
While the lubricant is beneficial for reducing the pressure (and power) required by the viscous material pump, the lubricant is often a substance which is undesirable in the final viscous material product. The benefit of easier pumping due to adding lubricant must be weighed against the detriment of having the lubricant in the viscous material flow. It is accordingly desired to minimize lubricant injection as much as possible while still providing the beneficial effects of the lubricant.
While viscous material lubrication systems have been effective in reducing the frictional loss of the viscous material flow, a significant lubricant pressure is needed to overcome back pressure and prevent backflow of the viscous material through the lubrication inlet. If the viscous material flow is not continuous (i.e., is not constant velocity), the back pressure provided by the viscous material to the lubrication inlet will not remain constant. Because of the varying velocity/pressure of the viscous material, neither a constant pressure nor a constant velocity flow of lubricant produces consistent lubricant application along the length of the viscous material plug. Constant velocity lubricant flow causes lubricant to be applied more heavily to locations along the viscous material plug which were stopped or moving slowly past the lubricant inlet. Constant pressure lubricant flow further adds to this problem, because the lubricant tends to flow faster when the plug is stopped or moving slower (i.e. with lower back pressure). Uncontrolled lubricant injection thus forms undesirable lubricant pockets in the viscous material. These effects are magnified if the viscous material is not of a homogenous consistency and compressibility. Accordingly, a system is desired to control lubricant injection such that it will more consistently lubricate a plug of viscous material in the pipeline.